Thylacocephala (Arthropoda: Crustacea?) from the Cretaceous of Lebanon and implications for Thylacocephalan systematics

An intensive study of a collection of arthropods from the Cretaceous of Lebanon, formerly referred to as stomatopod larvae, reveals that these forms belong to the problematical arthropod class Thylacocephala. The species Protozoea hilgendorfi, P. damesi, and Pseuderichthus cretaceus display defining thylacocephalan characters such as a carapace enclosing the entire body bearing a large anterior optic notch; three pairs of large, raptorial appendages; and a posterior battery of small swimming limbs associated with muscle segments. Unique characters of at least the genus Protozoea are the numerous 'pits' covering the entire carapace, elongated anterior rostral and posterior spines, and a dorsal hinge indicative of a truly bivalved carapace. We note several anatomical curiosities that provide some insight into the anatomy, ecology and phylogenetic relationships of these and other thylacocephalan species. Structures on the carapace surface of thylacocephalans may represent sensory organs comparable to the receptors seen on thecostracan crustaceans. The affinities of the three species described are still not entirely clear, but a phylogenetic analysis of the entire group may resolve this.